1. Field of the Invention
The present invention relates to a camera shutter unit adapted to a digital still camera or the like and, more particularly to a camera shutter unit which is separately provided with a shutter blade for opening and dosing an exposure aperture and a diaphragm blade for stopping down the aperture.
2. Description of the Related Art
Unexamined Japanese Patent Publication (koka) No.10-221740, for example, discloses a conventional camera shutter unit in which separately installed are a shutter blade opening and closing an exposure aperture wherethrough light passes and a diaphragm blade stopping down the aperture.
This camera shutter unit includes a shutter blade arranged at a periphery of the aperture so as to move back and forth to open and close the aperture, one electromagnetic drive source for driving the shutter blade, a diaphragm blade arranged so as to move back and forth to stop down the aperture and release the stopping-down, and another electromagnetic drive source for driving the diaphragm blade.
Thereupon, when respective electromagnetic drive sources start, the shutter blade moves back and forth between an opening position wherein the aperture is opened and a closing position wherein the aperture is closed to open and close the aperture and the diaphragm blade moves back and forth between a stopping-down position wherein the aperture is stopped down and an evacuating position wherein the aperture is not stopped down. Also, when respective electromagnetic drive sources are not energized, the shutter blade is held in either an opening or a closing position and the diaphragm blade is held in either stopping-down or evacuating position.
By the way, with respect to the above conventional camera shutter unit, separate drive sources are provided for driving the shutter blade and diaphragm blade. Therefore, the shutter blade and diaphragm blade can be driven separately without using a complicated linkage. However, since separate electromagnetic drive sources are provided, the unit is large-sized, heavyweight, high-cost or the like and consumes a large amount of power in accordance with the number of electromagnetic drive sources.
Also, upon drive of the diaphragm blade and so on, in case only the electromagnetic drive source starts to move to the diaphragm blade, when positioned in a predetermined stopping down position, the diaphragm blade might bounce and therefore, when stopping down rapidly, the response characteristic of diaphragm blade is not preferable.
In view of the foregoing, an object of the present invention is to provide a camera shutter unit which adopts a mechanism for interlocking a diaphragm blade with a shutter blade without complexity of the unit, whereby the shutter blade and diaphragm blade can function reliably being a small size, be lightweight, low-cost, or the like.
To achieve the above-mentioned object, a camera shutter unit according to the present invention comprises a base plate having an exposure aperture, a diaphragm blade arranged to be capable of moving between a stopping-down position wherein the aperture is stopped down and an evacuating position wherein the aperture is opened (is not stopped down), a shutter blade arranged to be capable of moving between an opening position wherein the aperture is opened and a dosing position wherein the aperture is dosed, and a drive-control mechanism for dive-controlling the shutter and diaphragm blades. The drive-control mechanism is composed of a single electromagnetic drive source which can drive the shutter and diaphragm blades so as to interlock the diaphragm blade with the shutter blade, and a restricting means for restricting movement of the shutter blade toward the dosing position when the diaphragm blade is positioned in the stopping-down position and for releasing its restriction by a predetermined or more level drive force which is generated by the electromagnetic drive source.
Accordingly, when the single electromagnetic drive source starts, the shutter blade moves from the opening position to the dosing position or from the dosing position to the opening position and the diaphragm blade moves from the evacuating position to the stopping-down position or from the stopping-down position to the evacuating position.
Hereupon, for example, in the case of one operating mode in which the shutter operation is carried out without the diaphragm blade stopping down, when the electromagnetic drive source starts so as to generate a predetermined or more level drive force with the shutter blade being in the opening position and the diaphragm blade being in the evacuating position, the shutter blade moves to the dosing position and the diaphragm blade moves to the stopping-down position. At this time, since the shutter blade immediately moves to the dosing position without staying in a way position, the stopping-down of the aperture is not carried out by only the diaphragm blade.
On the other hand, in the case of another operating mode in which the shutter operation is carried out after stopping down by the diaphragm blade, when the electromagnetic drive source starts, in the course that the diaphragm blade moves to the stopping-down position, the restricting means acts on the shutter blade to restrict the movement thereof toward the dosing position. In this condition, when the electromagnetic drive source generates a predetermined or more level drive force, its restriction is released, whereby only the shutter blade moves to the dosing position. In both operating modes above-mentioned, when the electromagnetic drive source starts in reverse, the shutter blade moves to the opening position and the diaphragm blade moves to the evacuating position.
Thus, the single electromagnetic drive source can drive the shutter and diaphragm blades and there is provided with the restricting means which can restrict movement of the shutter blade and can release its restriction, in accordance with the amount of drive force generated by the electromagnetic drive source. Therefore, the shutter and diaphragm blades can function reliably and the unit can become small size, lightweight, or the like.
In the above unit, the restricting means may be of a spring which urges the shutter blade toward the opening position when the shutter blade is positioned between the closing position and the way position wherein the diaphragm blade is in the stopping-down position.
Accordingly, when the single electromagnetic drive source starts to make the shutter blade move from the opening position to the closing position, the urging force of the spring restricts more movement of the shutter blade, whereby the diaphragm blade interlocked with the shutter blade is held in the stopping-down position. Further, when the electromagnetic drive source is energized to generate a predetermined or more level drive force, its restriction is released against the urging force of the spring, so that only the shutter blade moves to the dosing position. Thus, adoption of the single spring serving as a restricting means makes it possible to improve the reliability of function and to simplify the unit.
In the above unit, the electromagnetic drive source may be magnetic-urged so as to keep the shutter blade in the way position and keep the diaphragm blade in the stopping-down position, in a non-energized condition.
Accordingly, when the electromagnetic drive source is energized to generate drive force whereby the shutter blade reaches the way position and the diaphragm blade reaches the stopping-down position, the energizing of the electromagnetic drive source is stopped. As a result, the shutter blade is held in the way position and the diaphragm blade is held in the stopping-down position, by the force relationship between the magnetic force from the electromagnetic drive source and the force from the restricting means (the spring force), namely, by the force relationship in which this magnetic force does not release the restriction, whereby its restricting condition is kept. That is, since the stopping-down condition is kept with the electromagnetic drive source being non-energized, power consumption of the unit can be reduced.
In the above unit, the electromagnetic drive source may be magnetic-urged so as to keep the shutter blade in the opening position and keep the diaphragm blade in the evacuating position, in a non-energized condition.
Accordingly, when the electromagnetic drive source is energized to generate drive force whereby the shutter blade reaches the opening position and the diaphragm blade reaches the evacuating position, the energizing of the electromagnetic drive source is stopped. As a result, the magnetic force of the electromagnetic drive source keeps the shutter blade in the opening position and keeps the diaphragm blade in the evacuating position. That is, since the opening condition and releasing condition of the stopping-down are held in a non-energized condition, power consumption of the unit an be reduced.
In the above unit, the drive-control mechanism may comprise a control means for controlling the electromagnetic drive source, wherein this control means controls the electromagnetic drive source by generating plural pulses when making the diaphragm blade move to the stopping-down position.
Accordingly, when the drive force of the electromagnetic drive source makes the diaphragm blade move to the stopping-down position, the plural (for example, two times) pulse energizing-control restrains bouncing of the diaphragm blade. In other words, the behavior of diaphragm blade is converged in a short time, whereby the diaphragm blade is rapidly positioned in the stopping-down position
Also, in the above unit, the drive-control mechanism may comprise a control means for controlling the electromagnetic drive source, wherein this control means controls the electromagnetic drive source so as to decrease the amount of current (or voltage) during a predetermined energized time, when making the diaphragm blade move to the stopping-down position.
Accordingly, when the drive force of the electromagnetic drive source makes the diaphragm blade move to the stopping-down position, the energizing-control, which for example decreases current (or voltage) in the form of steps or continuously, prevents the diaphragm blade from bouncing or restrains it. In other words, the behavior of diaphragm blade is converge in a short time, whereby the diaphragm blade is rapidly positioned in the stopping-down position.